Anisotropic conductive sheet

ABSTRACT

Disclosed herein is an anisotropically conductive sheet capable of holding charge in its surfaces under an unpressurised state, and moving the charge held in the surface in a thickness-wise direction thereof in a state pressurised in the thickness-wise direction, thereby controlling the quantity of the charge at the surface.  
     This anisotropically conductive sheet comprises a sheet base composed of an elastomer and conductive particles exhibiting magnetism contained in the sheet base in a state oriented so as to arrange in rows in a thickness-wise direction of the sheet base, and dispersed in a plane direction thereof. Supposing that a volume resistivity in the thickness-wise direction under an unpressurised state is R 0 , and a volume resistivity in the thickness-wise direction in a state pressurised under a pressure of 1 g/mm 2  in the thickness-wise direction is R 1 , the volume resistivity R 1  is 1×10 7  to 1×10 12  Ω·m, and a ratio (R 0 /R 1 ) of the volume resistivity R 0  to the volume resistivity R 1  is 1×10 1  to 1×10 4 .

TECHNICAL FIELD

[0001] The present invention relates to an anisotropically conductivesheet exhibiting conductivity in its thickness-wise direction.

BACKGROUND ART

[0002] An anisotropically conductive sheet is a sheet exhibitingconductivity only in its thickness-wise direction or havingpressure-sensitive conductive conductor parts exhibiting conductivityonly in its thickness-wise direction when it is pressurised in thethickness-wise direction. Since the anisotropically conductive sheet hasfeatures that compact electrical connection can be achieved withoutusing any means such as soldering or mechanical fitting, and that softconnection is feasible with mechanical shock or strain absorbed therein,it is widely used as a connector for achieving electrical connectionbetween a circuit device, for example, a printed circuit board, and aleadless chip carrier, liquid crystal panel or the like in fields of,for example, electronic computers, electronic digital clocks, electroniccameras and computer key boards.

[0003] On the other hand, in electrical inspection of circuit devicessuch as printed circuit boards and semiconductor integrated circuits, itis conducted to cause an anisotropically conductive elastomer sheet tointerpose between an electrode region to be inspected of a circuitdevice, which is an inspection target, and an electrode region forinspection of a circuit board for inspection in order to achieveelectrical connection between electrodes to be inspected formed on onesurface of the circuit device to be inspected and electrodes forinspection formed on the surface of the circuit board for inspection.

[0004] As such anisotropically conductive elastomer sheets, there haveheretofore been known those of various structures.

[0005] For example, as anisotropically conductive elastomer sheetsexhibiting conductivity under an unpressurised state, there have beenknown those in which conductive fibers are arranged in a sheet basecomposed of insulating rubber in a state oriented so as to extend in athickness-wise direction of the sheet, those in which conductive rubberincorporating carbon black or metal powder and insulating rubber arealternately laminated along a plane direction (see Japanese PatentApplication Laid-Open No. 94495/1975), etc.

[0006] On the other hand, as anisotropically conductive elastomer sheetsexhibiting conductivity in a state pressurised in the thickness-wisedirection thereof, there have been known those obtained by uniformlydispersing metal particles in an elastomer (see Japanese PatentApplication Laid-Open No. 93393/1976), those obtained by unevenlydistributing particles of a conductive magnetic material in an elastomerto form many conductive path-forming parts extending in thethickness-wise direction thereof and insulating parts for mutuallyinsulating them (see Japanese Patent Application Laid-Open No.147772/1978), those with a difference in level defined between thesurface of conductive path-forming parts and insulating parts (seeJapanese Patent Application Laid-Open No. 250906/1986), etc.

[0007] In recent years, however, a sheet capable of holding charge inits surface under an unpressurised state, and moving the charge held inthe surface in a thickness-wise direction thereof when pressurised inthe thickness-wise direction, thereby controlling the quantity of thecharge at the surface is required in fields of electronic parts andelectronic part-applied instruments.

[0008] However, the conventional anisotropically conductive elastomersheets do not sufficiently satisfy such properties.

DISCLOSURE OF THE INVENTION

[0009] The present invention has been made on the basis of the foregoingcircumstances and has as its object the provision of an anisotropicallyconductive sheet capable of holding charge in its surface under anunpressurised state, and moving the charge held in the surface in athickness-wise direction thereof in a state pressurised in thethickness-wise direction, thereby controlling the quantity of the chargeat the surface.

[0010] According to the present invention, there is provided ananisotropically conductive sheet comprising a sheet base composed of anelastomer and conductive particles exhibiting magnetism contained in thesheet base in a state oriented so as to arrange in rows in athickness-wise direction of the sheet base, and dispersed in a planedirection thereof, wherein

[0011] supposing that a volume resistivity in the thickness-wisedirection under an unpressurised state is R₀, and a volume resistivityin the thickness-wise direction in a state pressurised under a pressureof 1 g/mm² in the thickness-wise direction is R₁,

[0012] the volume resistivity R₁ is 1×10⁷ to 1×10¹² Ω·m, and

[0013] a ratio (R₀/R₁) of the volume resistivity R₀ to the volumeresistivity R₁ is 1×10¹ to 1×10⁴.

[0014] In the anisotropically conductive sheet according to the presentinvention, the volume resistivity R₀ may preferably be 1×10⁹ to 1×10¹⁴Ω·m.

[0015] In the anisotropically conductive sheet according to the presentinvention, the surface resistivity may preferably be 1×10¹³ to 1×10¹⁶Ω/□ E(ohm/square)

[0016] In the anisotropically conductive sheet according to the presentinvention, the total area proportion occupied by a substance forming theconductive particles detected by the electronic probe microanalysis inone surface of the sheet may preferably be 15 to 60%.

[0017] According to the present invention, there is also provided ananisotropically conductive sheet comprising a sheet base composed of anelastomer and conductive particles exhibiting magnetism and a volumeresistivity of 1×10² to 1×10⁷ Ω·m contained in the sheet base in a stateoriented so as to arrange in rows in a thickness-wise direction of thesheet base, and dispersed in a plane direction thereof.

[0018] In the anisotropically conductive sheet according to the presentinvention, the conductive particles may preferably be composed offerrite.

[0019] In the anisotropically conductive sheet according to the presentinvention, a non-magnetic conductivity-imparting substance maypreferably be contained in the sheet base.

[0020] According to the anisotropically conductive sheets of the presentinvention, since the volume resistivity R₁ in the thickness-wisedirection in a state pressurised falls within a specified range, and theratio (R₀/R₁) of the volume resistivity R₀ in the thickness-wisedirection under an unpressurised state to the volume resistivity R₁falls within a specified range, the charge is held in its surface underan unpressurised state, and the charge held in the surface is moved inthe thickness-wise direction under a state pressurised in thethickness-wise direction, thereby controlling the quantity of the chargeat the surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a cross-sectional view for explanation illustrating theconstruction of an exemplary anisotropically conductive sheet accordingto the present invention.

[0022]FIG. 2 is a cross-sectional view for explanation illustrating astate that a sheet-forming material layer has been formed in a mold.

[0023]FIG. 3 is a cross-sectional view for explanation illustrating astate that a parallel magnetic field has been applied to thesheet-forming material layer in a thickness-wise direction thereof.

[0024]FIG. 4 is a explanatory view illustrating a device used in theevaluation of anisotropically conductive sheets as to electricalproperties in Examples.

DESCRIPTION OF CHARACTERS

[0025]1 Anisotropically conductive sheet, 10 Sheet base, 10ASheet-forming material layer, 20 Mold, 21 Top force, 22 Bottom force, 23Spacer, 40 Earth plate, 45 Roll, P Conductive particles

BEST MODE FOR CARRYING OUT THE INVENTION

[0026] The embodiments of the present invention will hereinafter bedescribed in details.

[0027]FIG. 1 is a cross-sectional view for explanation illustrating theconstruction of an anisotropically conductive sheet according to thepresent invention. This anisotropically conductive sheet is constructedby causing conductive particles P exhibiting magnetism to be containedin a sheet base 10 composed of an elastomer in a state oriented so as toarrange in rows in a thickness-wise direction of the sheet base 10, anddispersed in a plane direction of the sheet base 10.

[0028] The thickness of the sheet base 10 is, for example, 0.02 to 10mm, preferably 0.05 to 8 mm.

[0029] In the anisotropically conductive sheet according to the presentinvention, supposing that a volume resistivity in the thickness-wisedirection in a state pressurised under a pressure of 1 g/mm2 in thethickness-wise direction is R₁, the volume resistivity R₁ is 1×10⁷ to1×10¹² Ω·m, preferably 1×10⁸ to 1×10¹¹ Ω·m.

[0030] If this volume resistivity R₁ is lower then 1×10⁷ Ω·m, it isdifficult to control the quantity of the charge in the surface of theanisotropically conductive sheet, since discharge of the charge held inthe surface thereof or the charge of reversed charge is easy to occur.If this volume resistivity R₁ exceeds 1×10¹² Ω·m on the other hand, itis difficult to sufficiently discharge the charge held in the surface ofthe anisotropically conductive sheet when the anisotropically conductivesheet is pressurised in the thickness-wise direction.

[0031] In the anisotropically conductive sheet according to the presentinvention, supposing that a volume resistivity in the thickness-wisedirection under an unpressurised state is R₀, the volume resistivity R₀is preferably 1×10⁹ to 1×10¹⁴ Ω·m, particularly 1×10¹⁰ to 1×10¹³ Ω·m.

[0032] If this volume resistivity R₀ is lower then 1×10⁹ Ω·m, it may bedifficult in some cases to sufficiently hold the charge in the surfaceof the anisotropically conductive sheet. If this volume resistivity R₀exceeds 1×10¹⁴ Ω·m on the other hand, it is not preferred, since ittakes a considerably long time to hold a prescribed quantity of thecharge in the surface of the anisotropically conductive sheet, and inaddition, even when the charge is held in the surface of theanisotropically conductive sheet, discharge of the charge is easy tooccur.

[0033] In the anisotropically conductive sheet according to the presentinvention, a ratio (R₀/R₁) of the volume resistivity R₀ to the volumeresistivity R₁ is 1×10¹ to 1×10⁴, preferably 1×10² to 1×10³.

[0034] If this ratio (R₀/R₁) is lower than 1×10¹, a difference in theperformance for holding the charge in the surface under an unpressurisedstate and the performance for holding the charge in the surface in thestate pressurised in the thickness-wise direction in the anisotropicallyconductive sheet becomes small, and so it is difficult to control thequantity of the charge in the surface of the anisotropically conductivesheet. If this ratio (R₀/R₁) exceeds 1×10⁴ on the other hand, theelectric resistance in the thickness-wise direction in the state theanisotropically conductive sheet has been pressurised in thethickness-wise direction is too low, so that the charge held in thesurface is easily moved in the thickness-wise direction. As a result, itis difficult to control the quantity of the charge at the surface.

[0035] In the anisotropically conductive sheet according to the presentinvention, the surface resistivity is preferably 1×10¹³ to 1×10¹⁶ Ω/□,particularly 1×10¹⁴ to 1×10¹⁵ Q/□.

[0036] If this surface resistivity is lower than 1×10¹³ Ω/□, it may bedifficult in some cases to sufficiently hold the charge in the surfaceof the anisotropically conductive sheet. If this surface resistivityexceeds 1×10¹⁶ Ω/□ on the other hand, it is not prefered, since it takesa considerably long time to hold a prescribed quantity of the charge inthe surface of the anisotropically conductive sheet, and in addition,even when the charge is held in the surface of the anisotropicallyconductive sheet, discharge of the charge is easy to occur.

[0037] In the present invention, the volume resistivity R₀, volumeresistivity R₁ and surface resistivity of the anisotropically conductivesheet can be measured in the following manner.

[0038] Volume Resistivity R₀ and Surface Resistivity:

[0039] A disk-like surface electrode having a diameter of 16 mm isformed on one surface of an anisotropically conductive sheet by means ofa sputtering apparatus by using Au—Pd as a target, and a ring-likesurface electrode having an inner diameter of 30 mm, the central pointof which is substantially the same as that of the disk-like surfaceelectrode, is formed. On the other hand, a disk-like back surfaceelectrode having a diameter of 30 mm is formed on the other surface ofthe anisotropically conductive sheet at a position corresponding to thedisk-like surface electrode by means of the sputtering apparatus byusing Au—Pd as a target.

[0040] Voltage of 500 V is applied between the disk-like surfaceelectrode and the back surface electrode in a state that the ring-likesurface electrode has been connected to the ground, and a current valuebetween the disk-like surface electrode and the back surface electrodeis measured, and a volume resistivity R₀ is found from this currentvalue.

[0041] Further, voltage of 1000 V is applied between the disk-likesurface electrode and the ring-like surface electrode in a state thatthe back surface electrode has been connected to the ground, and acurrent value between the disk-like surface electrode and the ring-likesurface electrode is measured, and a surface resistivity is found fromthis current value.

[0042] Volume Resistivity R₁:

[0043] An anisotropically conductive sheet is placed on a gold platedelectrode plate having a diameter of 50 mm and a probe which has adisk-like electrode having a diameter of 16 mm and a ring-like electrodehaving an inner diameter of 30 mm, the central point of which issubstantially the same as that of the disk-like electrode, is pressedunder a pressure of 1 g/mm² against this anisotropically conductivesheet. Voltage of 250 V is applied between the electrode plate and thedisk-like electrode in a state that the ring-like electrode has beenconnected to the ground, and a current value between the electrode plateand the disk-like electrode is measured, and a volume resistivity R₁ isfound from this current value.

[0044] The elastomer forming the sheet base 10 is preferably aninsulating polymeric substance having a crosslinked structure. Variousmaterials may be used as curable polymeric substance-forming materialsusable for obtaining this crosslinked polymeric substance. Specificexamples thereof include conjugated diene rubbers such as polybutadienerubber, natural rubber, polyisoprene rubber, styrene-butadiene copolymerrubber and acrylonitrile-butadiene copolymer rubber, and hydrogenatedproducts thereof; block copolymer rubbers such asstyrene-butadiene-diene block copolymer rubber and styrene-isopreneblock copolymer rubber, and hydrogenated products thereof; and besideschloroprene rubber, urethane rubber, polyester rubber, epichlorohydrinrubber, silicone rubber, ethylene-propylene copolymer rubber andethylene-propylene-diene copolymer rubber.

[0045] When weather resistance is required for the obtainedanisotropically conductive sheet, any other materials than theconjugated diene rubbers are preferably used. It is particularlypreferred that silicone rubber be used from the viewpoints of moldingand processing ability and electrical properties.

[0046] As the silicone rubber, those obtained by crosslinking orcondensing liquid silicone rubber is preferred. The liquid siliconerubber preferably has a viscosity not higher than 10⁵ poises as measuredat a shear rate of 10⁻¹ sec and may be any of condensation type,addition type and those having a vinyl group or hydroxyl group. Asspecific examples thereof, may be mentioned dimethyl silicone rawrubber, methylvinyl silicone raw rubber and methylphenylvinyl siliconeraw rubber.

[0047] Among these, vinyl group-containing liquid silicone rubber (vinylgroup-containing dimethyl polysiloxane) is generally obtained bysubjecting dimethyldichlorosilane or dimethyldialkoxysilane tohydrolysis and condensation reaction in the presence ofdimethylvinylchlorosilane or dimethylvinylalkoxysilane and thenfractionating the reaction product by, for example, repeateddissolution-precipitation.

[0048] Liquid silicone rubber having vinyl groups at both terminalsthereof is obtained by subjecting a cyclic siloxane such asoctamethylcyclotetrasiloxane to anionic polymerization in the presenceof a catalyst, using, for example, dimethyldivinylsiloxane as apolymerization terminator and suitably selecting other reactionconditions (for example, amounts of the cyclic siloxane and thepolymerization terminator). As the catalyst for the anionicpolymerization, may be used an alkali such as tetramethylammoniumhydroxide or n-butylphosphonium hydroxide or a silanolate solutionthereof. The reaction is conducted at a temperature of, for example, 80to 130° C.

[0049] Such a vinyl group-containing dimethyl polysiloxane preferablyhas a molecular weight Mw (weight average molecular weight as determinedin terms of standard polystyrene; the same shall apply hereinafter) of10,000 to 40,000. The vinyl group-containing dimethyl polysiloxane alsopreferably has a molecular weight distribution index (a ratio Mw/Mn ofweight average molecular weight Mw as determined in terms of standardpolystyrene to number average molecular weight Mn as determined in termsof standard polystyrene; the same shall apply hereinafter) of at most 2from the viewpoint of the heat resistance of the obtained conductivepath device.

[0050] On the other hand, hydroxyl group-containing liquid siliconerubber (hydroxyl group-containing dimethyl polysiloxane) is generallyobtained by subjecting dimethyldichlorosilane or dimethyldialkoxysilaneto hydrolysis and condensation reaction in the presence ofdimethylhydrochlorosilane or dimethylhydroalkoxysilane and thenfractionating the reaction product by, for example, repeateddissolution-precipitation.

[0051] The hydroxyl group-containing liquid silicone rubber is alsoobtained by subjecting a cyclic siloxane to anionic polymerization inthe presence of a catalyst, using, for example,dimethylhydrochlorosilane, methyldihydrochlorosilane ordimethylhydroalkoxysilane as a polymerization terminator and suitablyselecting other reaction conditions (for example, amounts of the cyclicsiloxane and the polymerization terminator). As the catalyst for theanionic polymerization, may be used an alkali such astetramethylammonium hydroxide or n-butylphosphonium hydroxide or asilanolate solution thereof. The reaction is conducted at a temperatureof, for example, 80 to 130° C.

[0052] Such a hydroxyl group-containing dimethyl polysiloxane preferablyhas a molecular weight Mw of 10,000 to 40,000. The hydroxylgroup-containing dimethyl polysiloxane also preferably has a molecularweight distribution index of at most 2 from the viewpoint of the heatresistance of the obtained conductive path device.

[0053] In the present invention, either one of the above-described vinylgroup-containing dimethyl polysiloxane and hydroxyl group-containingdimethyl polysiloxane may be used, or both may be used in combination.

[0054] In the present invention, a curing catalyst may suitably be usedfor curing the polymeric substance-forming material. As such a curingcatalyst, may be used an organic peroxide, fatty acid azo compound,hydrosilylated catalyst or the like.

[0055] Specific examples of the organic peroxide used as the curingcatalyst include benzoyl peroxide, bisdicyclobenzoyl peroxide, dicumylperoxide and di-tert-butyl peroxide.

[0056] Specific examples of the fatty acid azo compound used as thecuring catalyst include azobisisobutyronitrile.

[0057] Specific examples of that used as the catalyst forhydrosilylation reaction include publicly known catalysts such asplatinic chloride and salts thereof, platinum-unsaturatedgroup-containing siloxane complexes, vinylsiloxane-platinum complexes,platinum-1,3-divinyltetramethyldisiloxane complexes, complexes oftriorganophosphine or phosphine and platinum, acetyl acetate platinumchelates, and cyclic diene-platinum complexes.

[0058] The amount of the curing catalyst used is suitably selected inview of the kind of the polymeric substance-forming material, the kindof the curing catalyst and other curing treatment conditions. However,it is generally 3 to 15 parts by weight per 100 parts by weight of thepolymeric substance-forming material.

[0059] As the conductive particles P contained in the sheet base 10,conductive particles exhibiting magnetism are used from the viewpoint ofthe fact that they can easily be oriented so as to arrange in rows inthe thickness-wise direction of the resulting anisotropically conductivesheet 10 by applying a magnetic field thereto.

[0060] Specific examples of such conductive particles P include:

[0061] particles composed of metals exhibiting magnetism, such asnickel, iron and cobalt, particles of alloys thereof, particlescontaining such metals, and particles obtained by using these particlesas core particles and plating surfaces of the core particles with aconductive metal which is resistive to be oxidized, such as gold,silver, palladium or rhodium;

[0062] particles composed of ferromagnetic intermetallic compounds suchas ZrFe₂, FeBe₂, FeRh, MnZn, Ni₃Mn, FeCo, FeNi, Ni₂Fe, MnPt₃, FePd,FePd₃, Fe₃Pt, FePt, CoPt, CoPt₃ and Ni₃Pt, and particles obtained byusing these particles as core particles and plating surfaces of the coreparticles with a conductive metal which is resistive to be oxidized,such as gold, silver, palladium or rhodium;

[0063] particles composed of ferromagnetic metal oxides, such as ferriterepresented by the chemical formula: M¹O.Fe₂O₃ (wherein M¹ means a metalsuch as Mn, Fe, Ni, Cu, Zn, Mg, Co or Li), or mixtures (for example,Mn—Ze ferrite, Ni—Zn ferrite, etc.) thereof, manganite such as FeMn₂O₄,cobaltite represented by the chemical formula: M²O.Co₂O₃ (wherein M²means a metal such as Fe or Ni), Ni_(0.5)Zn_(0.5)Fe₂O₄,Ni_(0.35)Zn_(0.65)Fe₂O₄, Ni_(0.7)Zn_(0.2)Fe_(0.1)Fe₂O₄, andNi_(0.5)Zn_(0.4)Fe_(0.1)Fe₂O₄, and particles obtained by using theseparticles as core particles and plating surfaces of the core particleswith a conductive metal which is resistive to be oxidized, such as gold,silver, palladium or rhodium;

[0064] particles obtained by using particles of a non-magnetic metal,particles composed of an inorganic substance such as glass beads orcarbon, or particles composed of a polymer such as polystyrene orpolystyrene crosslinked by divinylbenzene as core particles and platingsurfaces of the core particles with a conductive magnetic material suchas nickel or cobalt; and particles obtained by coating the coreparticles with both conductive magnetic material and conductive metalwhich is resistive to be oxidized.

[0065] Among these conductive particles, conductive particles having avolume resistivity (hereinafter referred to as “volume resistivityR_(p)”) of 1×10² to 1×10⁷ Ω·m, particularly 1×10³ to 1×10⁶ Ω·m arepreferably used in that an anisotropically conductive sheet, the volumeresistivity R₀ and volume resistivity R₁ of which satisfy the aboveconditions, is certainly obtained. Specifically, conductive particlescomposed of ferrite represented by the chemical formula: M¹O.Fe₂O₃(wherein M¹ means a metal such as Mn, Fe, Ni, Cu, Zn, Mg, Co or Li), ormixtures (for example, Mn—Ze ferrite, Ni—Zn ferrite or the like) thereofare preferably used.

[0066] These conductive particles may be those on the surfaces of whichan insulating coating has been formed for the purpose of adjusting theconductivity thereof. For the insulating coating, may be used aninorganic material such as a metal oxide or silicon oxide compound, oran organic material such as a resin or coupling agent.

[0067] In the present invention, the volume resistivity R_(p) of theconductive particles can be measured in the following manner.

[0068] A closed-end cylindrical cell having an inner diameter of 25 mm,a depth of 50 mm and a bottom formed by an electrode having a diameterof 25 mm is charged with the conductive particles, and the conductiveparticles are pressed under a pressure of 127 kg/cm² by a columnarelectrode having a diameter of 25 mm. In this state, voltage of 100 V isapplied between the electrodes to measure a current value and a distancebetween the electrodes, thereby finding a volume resistivity R_(p) fromthese values.

[0069] The number average particle diameter of the conductive particlesP is preferably 1 to 1,000 em, more preferably 2 to 500 μm, still morepreferably 5 to 300 μm, particularly preferably 10 to 200 μm.

[0070] When the resulting anisotropically conductive sheet is requiredto have smaller intervals among conductive paths formed in athickness-wise direction thereof by the conductive particles P, i.e.,high-resolution anisotropic conductivity, those having a smaller numberaverage particle diameter are preferably used as the conductiveparticles P. Specifically, conductive particles having a number averageparticle diameter of 1 to 20 μm, particularly 1 to 10 μm are preferablyused.

[0071] The particle diameter distribution (Dw/Dn) of the conductiveparticles P is preferably 1 to 10, more preferably 1.01 to 7, still morepreferably 1.05 to 5, particularly preferably 1.1 to 4.

[0072] When conductive particle satisfying such conditions are used, theresulting anisotropically conductive sheet becomes easy to deform underpressure, and sufficient electrical contact is achieved among theconductive particles.

[0073] No particular limitation is imposed on the shape of theconductive particles P. However, they are preferably in the shape of asphere or star, or a mass of secondary particles obtained by aggregatingthese particles from the viewpoint of permitting easy dispersion ofthese particles in the polymeric substance-forming material.

[0074] The content of water in the conductive particles P is preferablyat most 5%, more preferably at most 3%, still more preferably at most2%, particularly preferably at most 1%. The use of conductive particlessatisfying such conditions can prevent or inhibit the occurrence ofbubbles upon the curing treatment of the polymeric substance-formingmaterial.

[0075] The proportion of the conductive particles P in the sheet base 10is suitably selected according to the intended end application of theresulting anisotropically conductive sheet and the kind of theconductive particles used. However, it is preferably selected from arange of generally 3 to 50%, preferably 5 to 30 in terms of volumefraction. If this proportion is lower than 3%, it may be difficult insome cases to form conductive paths sufficiently low in electricresistance. If the proportion exceeds 50% on the other hand, theresulting conductive sheet tends to become brittle.

[0076] In the anisotropically conductive sheet according to the presentinvention, the total area proportion of regions in which a substanceforming the conductive particles P has been detected when an elementalanalysis test has been conducted by the electronic probe microanalysis(EPMA) in one surface of the sheet is preferably 15 to 60%, particularly25 to 45% based on the whole area of the object regions to be tested.

[0077] When this proportion is lower than 15%, the proportion of theconductive particles P present at the surface of such an anisotropicallyconductive sheet or in the vicinity thereof is low, and so the volumeresistivity R₁ thereof becomes high. As a result, it may be difficult insome cases to control the quantity of charge at the surface of theanisotropically conductive sheet, and it is necessary to pressurise theanisotropically conductive sheet by a higher pressure for the purpose ofachieving conductivity necessary in the thickness-wise directionthereof. Such a low proportion is hence not preferable. If thisproportion exceeds 60% on the other hand, the proportion of theconductive particles P present at the surface of such an anisotropicallyconductive sheet or in the vicinity thereof is high, and so the volumeresistivity R₀ in the thickness-wise direction under the unpressurisedstate, and the surface resistivity are liable to be low.

[0078] Specifically, the total area proportion of regions, in which asubstance forming the conductive particles P have been detected, can bemeasured by means of an “Electron Beam Microanalizer EPMA-8705”manufactured by Shimadzu Corporation in the following manner.

[0079] An anisotropically conductive sheet is placed on an X-Y samplestage, and one surface of the anisotropically conductive sheet is thenirradiated with an electron beam to detect characteristic X-raysgenerated thereby to conduct an elementary analysis. As specificconditions, the dimension of an irradiation spot of the electron beam is1 μm×1 μm, the uptake time of the characteristic X-rays is 10 msec, andthe detection depth of elements is about 2 μm from the surface of theanisotropically conductive sheet. The X-Y sample stage is moved 1 μm by1 μm in an X direction or Y direction, thereby conducting irradiation ofthe electron beam, detection of the characteristic X-rays and elementaryanalysis as to 512×512 points in total. From the results of theelementary analysis as to 512 μm×512 μm object regions to be tested atone surface of the anisotropically conductive sheet measured in such amanner, a map indicating regions, in which the substance forming theconductive particles has been detected in the object regions to betested, is prepared. The map is then subjected to image-analysis,thereby finding a proportion of the total area of the regions, in whichthe substance forming the conductive particles P has been detected, tothe area of the object regions to be tested.

[0080] In the anisotropically conductive sheet according to the presentinvention, a non-magnetic conductivity-imparting substance may bedispersed in the sheet base 10, as needed, for the purpose ofcontrolling the values of the volume resistivity R₀, volume resistivityR₁ and surface resistivity.

[0081] As such a non-magnetic conductivity-imparting substance, may beused a substance exhibiting conductivity by itself (hereinafter may alsobe referred to as “self-conductive substance”), a substance developingconductivity by absorbing moisture (hereinafter may also be referred toas “hygroscopic conductive substance”) or the like. Theseself-conductive and hygroscopic conductive substances may be used eithersingly or in any combination thereof.

[0082] The self-conductive substance may be generally chosen for usefrom substances exhibiting conductivity by free electrons in a metallicbond, substances undergoing charge transfer by transfer of excesselectrons, substances undergoing charge transfer by hole transfer,organopolymeric substances having n-bonds along a main chain to exhibitconductivity by interaction thereof, substances undergoing chargetransfer by interaction of groups present in side chains, etc.Specifically, non-magnetic metals such as platinum, gold, silver,copper, aluminum, manganese, zinc, tin, lead, indium, molybdenum,niobium, tantalum and chromium; non-magnetic conductive metal oxidessuch as copper dioxide, zinc oxide, tin oxide and titanium oxide;conductive fibrous substances such as whisker, potassium titanate andcarbon; semiconductive substance such as germanium, silicon, indiumphosphide and zinc sulfide; carbonaceous substances such as carbon blackand graphite; conductive polymeric substances such as polyacetylenepolymers, polyphenylene polymers and heterocyclic polymers such asthiophenylene polymers; etc. may be used. These substances may be usedas the conductivity-imparting substances either singly or in anycombination thereof.

[0083] The hygroscopic conductive substance may be chosen for use fromsubstances forming an ion to transfer charge by the ion, substanceshaving a group high in polarity, such as a hydroxyl group or estergroup, etc.

[0084] Specifically, substances forming a cation, such as quaternaryammonium salts and amine compounds; substances forming an anion, such asaliphatic sulfonic acid salts, higher alcohol sulfate salts, higheralcohol ethylene oxide-added sulfate salts, higher alcohol phosphatesalts and higher alcohol ethylene oxide-added phosphate salts;substances forming both cation and anion, such as betaine compounds;silicon compounds such as polychlorosiloxane, alkoxysilane,polyalkoxysilane and polyalkoxysiloxane; polymeric substances such asconductive urethane, polyvinyl alcohol and copolymers thereof; alcoholicsurfactants such as higher alcohol ethylene oxides, polyethylene glycolfatty acid esters and polyhydric alcohol fatty acid esters; substanceshaving a group high in polarity, such as polysaccharides; etc. may beused. These substances may be used as the conductivity-impartingsubstances either singly or in any combination thereof.

[0085] Among the hygroscopic conductive substances, the aliphaticsulfonic acid salts are preferred in that they have high heatresistance, are good in compatibility with elastic polymeric substances,and do not cause polymerization inhibition in the formation of anelastic polymeric substance.

[0086] As such aliphatic sulfonic acid salts, are preferred those havingan alkyl group having 10 to 20 carbon atoms, such as 1-decanesulfonates,1-undecanesulfonates, 1-dodecanesulfonates, 1-tridecanesulfonate,1-tetradecane-sulfonates, 1-pentadecanesulfonates,1-hexadecanesulfonates, 1-heptadecanesulfonates, 1-octadecanesulfonates,1-nonadecanesulfonates and 1-eicosanedecasulfonates, and isomersthereof. As the salts, are preferred salts with alkali metals such aslithium, sodium and potassium, with the sodium salts being particularlypreferred in that they have highest heat resistance.

[0087] A proportion of the non-magnetic conductivity-imparting substancein the conductive elastomer is suitably set according to the kind of theconductivity-imparting substance, the degree of intended conductivity,etc. However, it is generally set from a range of 0.2% by weight orlower, preferably 0.01 to 0.1% by weight when the non-magnetic metal isused singly as the conductivity-imparting substance, 1% by weight orlower, preferably 0.05 to 0.5% by weight when the non-magneticconductive metal oxide is used singly as the conductivity-impartingsubstance, 0.5% by weight or lower, preferably 0.02 to 0.2% by weightwhen the conductive fibrous substance is used singly as theconductivity-imparting substance, 1% by weight or lower, preferably 0.08to 0.8% by weight when the carbon black is used singly as theconductivity-imparting substance, 0.8% by weight or lower, preferably0.05 to 0.5% by weight when the conductive polymeric substance is usedsingly as the conductivity-imparting substance, or 1% by weight orlower, preferably 0.08 to 0.8% by weight when the hygroscopic conductivesubstance is used singly as the conductivity-imparting substance. Whenthe above various conductivity-imparting substances are used incombination, the proportions thereof are set in view of the aboverespective ranges.

[0088] In the conductive elastomer, may be contained a general inorganicfiller such as silica powder, colloidal silica, aerogel silica oralumina as needed. By containing such an inorganic filler, thethixotropic property of the material for forming the sheet base 10 isensured, the viscosity thereof becomes high, the dispersion stability ofthe conductive particles is enhanced, and moreover the strength of theresulting sheet base 10 is enhanced.

[0089] No particular limitation is imposed on the amount of such aninorganic filler used. However, the use in a large amount is notpreferred because the orientation of the conductive particles by amagnetic field cannot be fully achieved.

[0090] Such an anisotropically conductive sheet can be produced, forexample, in the following manner.

[0091] A flowable sheet-forming material with conductive particlesexhibiting magnetism and an optionally used non-magneticconductivity-imparting substance dispersed in a liquid polymericsubstance-forming material, which will become an insulating elasticpolymeric substance by a curing treatment, is first prepared, and thesheet-forming material is filled into a mold 20 as illustrated in FIG.2, thereby forming a sheet-forming material layer 10A.

[0092] The mold 20 is so constructed that a top force 21 and a bottomforce 22 each composed of a rectangular ferromagnetic plate are arrangedso as to be opposed to each other through a rectangular frame-likespacer 23. A mold cavity is defined between the lower surface of the topforce 21 and the upper surface of the bottom force 22.

[0093] Electromagnets or permanent magnets, for example, are thenarranged on the upper surface of the top force 21 and the lower surfaceof the bottom force 22 to apply a parallel magnetic field to thesheet-forming material layer 10A in the mold in the thickness-wisedirection thereof. As a result, in the sheet-forming material layer 10A,the conductive particles P dispersed in the sheet-forming material layerare oriented so as to arrange in rows in a thickness-wise direction ofthe sheet-forming material layer while retaining a state dispersed in aplane direction as illustrated in FIG. 3. When the non-magneticconductivity-imparting substance is contained in the sheet-formingmaterial layer 10A, the conductivity-imparting substance remains a statedispersed in the sheet-forming material layer 10A even when the parallelmagnetic field is applied.

[0094] In this state, the sheet-forming material layer 10A is subjectedto a curing treatment, thereby obtaining an anisotropically conductivesheet comprising a sheet base composed of the insulating elastomer andthe conductive particles P contained in the sheet base in a stateoriented so as to arrange in rows in a thickness-wise direction thereof.

[0095] In the above-described process, the intensity of the parallelmagnetic field applied to the sheet-forming material layer 10A ispreferably an intensity that it amounts to 0.02 to 1.5 T on the average.

[0096] When the parallel magnetic field is applied in a thickness-wisedirection of the sheet-forming material layer 10A by the permanentmagnets, those composed of alunico (Fe—Al—Ni—Co alloy), ferrite or thelike are preferably used as the permanent magnets in that the intensityof the parallel magnetic field within the above range is achieved.

[0097] The curing treatment of the sheet-forming material layer 10A maybe conducted in the state that the parallel magnetic field has beenapplied. However, the treatment may also be conducted after stopping theapplication of the parallel magnetic field.

[0098] The curing treatment of the sheet-forming material layer 10A issuitably selected according to the material used. However, the treatmentis generally conducted by a heat treatment. Specific heating temperatureand heating time are suitably selected in view of the kind of thepolymeric substance-forming material making up the sheet-formingmaterial layer 10A, and the like, the time required for movement of theconductive particles P, and the like.

[0099] According to the anisotropically conductive sheet of theabove-described constitution, the volume resistivity R₁ in thethickness-wise direction in a state pressurised falls within a specifiedrange, and the ratio of the volume resistivity R₀ in the thickness-wisedirection under an unpressurised state to the volume resistivity R₁falls within a specified range, and so the charge can be held in itssurface under the unpressurised state, and the charge held in thesurface can be moved in the thickness-wise direction in a statepressurised in the thickness-wise direction, thereby controlling thequantity of the charge in the surface.

[0100] A member to be connected is brought into contact with one surfaceof such an anisotropically conductive sheet according to the presentinvention, whereby a state of microscopic surface distribution of aquantity of electricity such as static electricity, electrostaticcapacity or ionic quantity in the surface of the member to be connectedcan be transferred to and held in the surface of the anisotropicallyconductive sheet. Further, the member to be connected is pressed againstone surface of the anisotropically conductive sheet, the state ofmicroscopic surface distribution of the quantity of electricitytransferred and held can be moved to the other surface of theanisotropically conductive sheet.

[0101] Specifically, the anisotropically conductive sheet according tothe present invention is useful as a sensor part for shifting theelectrostatic capacity distribution of the surface of an inspectiontarget to an instrumentation part in, for example, an electricalinspection apparatus of an electrostatic capacity system for printedwiring boards or the like. According to such an electrical inspectionapparatus, the electrostatic capacity distribution of the surface of theinspection target can be expressed as a two-dimensional image.

[0102] In addition, for example, a pattern image of ions generated froma writing apparatus such as a laser printer or an electrostatic patternimage at a roll part in an electronic copying machine can be convertedinto an electrical pattern image through the anisotropically conductivesheet according to the present invention.

[0103] According to the anisotropically conductive sheet according tothe present invention, a state of microscopic surface distribution of aquantity of electricity such as static electricity, electrostaticcapacity or ionic quantity can be expressed as a two-dimensionalelectrical pattern image without being limited to the above-describedexample.

[0104] The anisotropically conductive sheet according to the presentinvention can be utilized for various uses, to which the conventionalanisotropically conductive sheets are applied, for example, as aconnector for achieving electrical connection between circuit devices ora connector used in electrical inspection of circuit devices.

[0105] The anisotropically conductive sheet according to the presentinvention can also be used as a heat-conductive sheet such as aheat-radiating sheet because chains of the conductive particles Pfunction as heat-conductive paths when proper particles are used as theconductive particles P.

[0106] For example, the anisotropically conductive sheet according tothe present invention is brought into contact with a heating medium suchas a heating part of an electron device, and the anisotropicallyconductive sheet is intermittently repeatedly pressurised in athickness-wise direction thereof, whereby a certain quantity of heat isradiated from the heating medium through the anisotropically conductivesheet. As a result, the temperature of the heating medium can be keptconstant.

[0107] The anisotropically conductive sheet according to the presentinvention can further be used as a sheet for absorbing electromagneticradiation, whereby electromagnetic noises caused from, for example, anelectronic part or the like can be reduced.

[0108] The present invention will hereinafter be described specificallyby the following examples. However, the present invention is not limitedto these examples.

[0109] In the following examples and comparative examples, the volumeresistivities R_(p) of conductive particles were measured by means of a“Powder Resistance Measuring System MCP-PD41” manufactured by MitsubishiKagaku K.K.

EXAMPLE 1

[0110] Eighty parts by weight of conductive particles were added to andmixed with 100 parts by weight of addition type liquid silicone rubber,thereby preparing a sheet-forming material.

[0111] In the above preparation, particles (“KNS-415”, product of TodaKogyo K.K.; number average particle diameter: 5 μm, volume resistivityR_(p): 5×10⁴ Ω·m) composed of MnFe₃O₄ (manganese ferrite) were used asthe conductive particles.

[0112] A mold for molding of anisotropically conductive sheets, composedof a top force and a bottom force each formed of a rectangular ironplate having a thickness of 5 mm and a rectangular frame-like spacerhaving a thickness of 0.5 mm was provided. The sheet-molding materialprepared above was charged into a cavity of the mold to form asheet-forming material layer. While arranging electromagnets on theupper surface of the top force and the lower surface of the bottom forceto apply a parallel magnetic field of 1 T to the sheet-forming materiallayer in the thickness-wise direction thereof, the sheet-formingmaterial layer was subjected to a curing treatment under conditions of100° C. for 2 hours, thereby forming a sheet base having a thickness of0.5 mm to produce an anisotropically conductive sheet of theconstitution illustrated in FIG. 1.

[0113] A proportion of the conductive particles in the sheet base inthis anisotropically conductive sheet was 20% in terms of volumefraction.

[0114] The total area proportion occupied by a substance forming theconductive particles detected by the electronic probe microanalysis inone surface of this anisotropically conductive sheet was 40%.

EXAMPLE 2

[0115] Hundred parts by weight of conductive particles were added to andmixed with 100 parts by weight of addition type liquid silicone rubber,thereby preparing a sheet-forming material.

[0116] In the above preparation, particles (“IR-BO”, product of TDKK.K.; number average particle diameter: 14 μm, volume resistivity R_(p):2×10⁵ Ω·m) composed of manganese ferrite were used as the conductiveparticles.

[0117] A sheet base having a thickness of 0.5 mm was formed in the samemanner as in Example 1 except that this sheet-forming material was used,thereby producing an anisotropically conductive sheet of theconstitution illustrated in FIG. 1.

[0118] A proportion of the conductive particles in the sheet base inthis anisotropically conductive sheet was 25% in terms of volumefraction.

[0119] The total area proportion occupied by a substance forming theconductive particles detected by the electronic probe microanalysis inone surface of this anisotropically conductive sheet was 45%.

EXAMPLE 3

[0120] Hundred parts by weight of conductive particles and 0.5 parts byweight of a non-magnetic conductivity-imparting substance were added toand mixed with 100 parts by weight of addition type liquid siliconerubber, thereby preparing a sheet-forming material.

[0121] In the above preparation, particles (“IR-BO”, product of TDKK.K.; number average particle diameter: 14 μm, volume resistivity R_(p):2×10⁵ Ω·m) composed of manganese ferrite were used as the conductiveparticles, and sodium alkanesulfonate (hygroscopic conductivesubstance), the alkyl group of which has 5 to 15 carbon atoms, was usedat the non-magnetic conductivity-imparting substance.

[0122] A sheet base having a thickness of 0.5 mm was formed in the samemanner as in Example 1 except that this sheet-forming material was used,thereby producing an anisotropically conductive sheet of theconstitution illustrated in FIG. 1.

[0123] A proportion of the conductive particles in the sheet base inthis anisotropically conductive sheet was 25% in terms of volumefraction.

[0124] The total area proportion occupied by a substance forming theconductive particles detected by the electronic probe microanalysis inone surface of this anisotropically conductive sheet was 45%.

COMPARATIVE EXAMPLE 1

[0125] Two hundred and ten parts by weight of conductive particles wereadded to and mixed with 100 parts by weight of addition type liquidsilicone rubber, thereby preparing a sheet-forming material.

[0126] In the above preparation, nickel particles (“SF-300”, product ofWestaim Co.; number average particle diameter: 42 μm, volume resistivityR_(p): 0.1 Ω·m) were used as the conductive particles.

[0127] A sheet base having a thickness of 0.5 mm was formed in the samemanner as in Example 1 except that this sheet-forming material was used,thereby producing an anisotropically conductive sheet of theconstitution illustrated in FIG. 1.

[0128] A proportion of the conductive particles in the sheet base inthis anisotropically conductive sheet was 20% in terms of volumefraction.

[0129] The total area proportion occupied by a substance forming theconductive particles detected by the electronic probe microanalysis inone surface of this anisotropically conductive sheet was 35%.

COMPARATIVE EXAMPLE 2

[0130] Fifteen parts by weight of a conductivity-imparting substancewere added to and mixed with 100 parts by weight of addition type liquidsilicone rubber, thereby preparing a sheet-forming material.

[0131] In the above preparation, carbon black (self-conductivesubstance) produced by Denki Kagaku K.K. was used as theconductivity-imparting substance.

[0132] A sheet base having a thickness of 0.5 mm was formed in the samemanner as in Example 1 except that this sheet-forming material was used,thereby producing an anisotropically conductive sheet.

COMPARATIVE EXAMPLE 3

[0133] Thirty parts by weight of a conductivity-imparting substance wereadded to and mixed with 100 parts by weight of addition type liquidsilicone rubber, thereby preparing a sheet-forming material.

[0134] In the above preparation, a mixture of 20 parts by weight ofcarbon black (self-conductive substance) produced by Denki Kagaku K.K.and 10 parts by weight of sodium alkanesulfonate (hygroscopic conductivesubstance), the alkyl group of which has 5 to 15 carbon atoms, were usedas the conductivity-imparting substance.

[0135] A sheet base having a thickness of 0.5 mm was formed in the samemanner as in Example 1 except that this sheet-forming material was used,thereby producing an anisotropically conductive sheet.

[0136] <Electric Resistance>

[0137] With respect to each of the anisotropically conductive sheetsaccording to Examples 1 to 3 and Comparative Examples 1 to 3, the volumeresistivity R₀, volume resistivity R₁ and surface resistivity weremeasured by means of a “Hirester UP” manufactured by Mitsubishi KagakuK.K. in the following manner.

[0138] Volume Resistivity R₀ and Surface Resistivity:

[0139] A disk-like surface electrode having a diameter of 16 mm and athickness of 0.2 μm was formed on one surface of the anisotropicallyconductive sheet by means of an ion sputtering apparatus (E1010,manufactured by Hitachi Science K.K.) by using Au—Pd as a target, and aring-like surface electrode having an inner diameter of 30 mm and athickness of 0.2 μm, the central point of which was substantially thesame as that of the disk-like surface electrode, was formed. On theother hand, a disk-like back surface electrode having a diameter of 30mm and a thickness of 0.2 μm was formed on the other surface of theanisotropically conductive sheet at a position corresponding to thedisk-like surface electrode by means of the ion sputtering apparatus(E1010, manufactured by Hitachi Science K.K.) by using Au—Pd as atarget.

[0140] Voltage of 500 V was applied between the disk-like surfaceelectrode and the back surface electrode in a state that the ring-likesurface electrode had been connected to the ground, and a current valuebetween the disk-like surface electrode and the back surface electrodewas measured, and a volume resistivity R₀ was found from this currentvalue.

[0141] Further, voltage of 1000 V was applied between the disk-likesurface electrode and the ring-like surface electrode in a state thatthe back surface electrode had been connected to the ground, and acurrent value between the disk-like surface electrode and the ring-likesurface electrode was measured, and a surface resistivity was found fromthis current value.

[0142] Volume Resistivity R₁:

[0143] The anisotropically conductive sheet was placed on a gold platedelectrode plate having a diameter of 50 mm, and a probe which had adisk-like electrode having a diameter 5 of 16 mm and a ring-likeelectrode having an inner diameter of 30 mm, the central point of whichwas substantially the same as that of the disk-like surface electrode,was pressed under a pressure of 1 g/mm² against this anisotropicallyconductive sheet. Voltage of 250 V was 10 then applied between theelectrode plate and the disk-like electrode in a state that thering-like electrode had been connected to the ground, and a currentvalue between the electrode plate and the disk-like electrode wasmeasured, and a volume resistivity R₁ was found from this current value.

[0144] The results are shown in Table 1. TABLE 1 Volume resistivitySurface (Ω · m) Ratio resistivity R₀ R₁ (R₀/R₁) (Ω/□) Example 1 1 × 10¹¹1 × 10⁹  1 × 10³ 1 × 10¹⁵ Example 2 1 × 10¹² 1 × 10¹⁰ 1 × 10² 1 × 10¹⁶Example 3 1 × 10¹⁰ 1 × 10⁸  1 × 10⁴ 1 × 10¹⁴ Comparative 1 × 10⁸  1 ×10⁵  1 × 10³ 1 × 10¹² Example 1 Comparative 8 × 10⁷  6 × 10⁶  13 2 ×10¹³ Example 2 Comparative 8 × 10⁵  4 × 10⁵  2 4 × 10⁶  Example 3

[0145] <Charge Holding Ability and Mobility>

[0146] With respect to each of the anisotropically conductive sheetsaccording to Examples 1 to 3 and Comparative Examples 1 to 3, the chargeholding ability in the surface thereof and the charge mobility at thetime the sheet was pressurised in the thickness-wise direction thereofwere examined in the following manner.

[0147] The anisotropically conductive sheet 1 was arranged on an earthplate 40 as illustrated in FIG. 4, and a roll 45 made of a urethaneresin was arranged just over the anisotropically conductive sheet 1.This roll 45 is such that charge has been accumulated on the surfacethereof by a discharge treatment with a Tesla coil, and the surfacepotential thereof is controlled within a range of 500±50 V (a valuemeasured by means of a surface potentiometer “Model 520-1” manufacturedby Trec Japan).

[0148] The roll 45 was gradually lowered, thereby bringing it intocontact with the surface of the anisotropically conductive sheet 1 (anunpressurised state). After retaining this state for 1 minute, the rollwas gradually lifted and the surface potential of the anisotropicallyconductive sheet 1 was measured by means of the surface potentiometer“Model 520-1”.

[0149] Next, the roll 45 was gradually lowered, thereby pressurising thesurface of the anisotropically conductive sheet 1 under a pressure of 1g/mm². After retaining this state for 1 minute, the roll 45 wasgradually lifted to measure the surface potential of the anisotropicallyconductive sheet 1 by means of the surface potentiometer “Model 520-1”.

[0150] The above-described process was repeated 10 times in total tofind an average value of the surface potential and a scatter of themeasured values.

[0151] The results are shown in Table 2. TABLE 2 surface potential (v)an unpressurised a pressurised state state Example 1 420 ± 40 100 ± 20Example 2 450 ± 50 120 ± 20 Example 3 400 ± 40  90 ± 10 Comparative  70± 30  60 ± 30 Example 1 Comparative  60 ± 30  50 ± 30 Example 2Comparative  50 ± 30  40 ± 30 Example 3

[0152] As apparent from the results shown in Table 2, according to theanisotropically conductive sheets of Examples 1 to 3, it was confirmedthat the charge on the surface of the roll 45 is surely transferred tothe surface of the anisotropically conductive sheet and held therein bybringing the surface of the roll 45 into contact with the surface ofeach anisotropically conductive sheet. It was also confirmed that thecharge on the surface of the roll 45 is moved to the earth plate throughthe anisotropically conductive sheet, and the quantity of the charge inthe surface of the roll is thereby controlled by pressurising thesurface of the anisotropically conductive sheet with the roll 45.

[0153] In the anisotropically conductive sheet of Comparative Example 1on the other hand, the charge on the surface is easily moved even underthe unpressurised state because the volume resistivity R₀, volumeresistivity R₁ and surface resistivity thereof are all low. Accordingly,there is no difference in the performance of holding the charge in thesurface between the unpressurised state and the state pressurised in thethickness-wise direction. As a result, it was difficult to control thequantity of the charge at the surface.

[0154] In the anisotropically conductive sheet of Comparative Example 2,the charge on the surface is easily moved even under the unpressurisedstate because the volume resistivity R₀ and volume resistivity R₁thereof are both low. Accordingly, there is no difference in theperformance of holding the charge in the surface between theunpressurised state and the state pressurised in the thickness-wisedirection. As a result, it was difficult to control the quantity of thecharge at the surface.

[0155] In the anisotropically conductive sheet of Comparative Example 3,the charge on the surface is easily moved even under the unpressurisedstate because the volume resistivity R₀, volume resistivity R₁, ratio(R₀/R₁) and surface resistivity thereof are all low. Accordingly, thereis no difference in the performance of holding the charge in the surfacebetween the unpressurised state and the state pressurised in thethickness-wise direction. As a result, it was difficult to control thequantity of the charge at the surface.

[0156] Effect of the Invention

[0157] According to the present invention, as described above, there canbe provided anisotropically conductive sheets capable of holding thecharge in their surfaces under an unpressurised state, and moving thecharge held in the surfaces in a thickness-wise direction thereof in astate pressurised in the thickness-wise direction, thereby controllingthe quantity of the charge at the surfaces.

1 An anisotropically conductive sheet comprising a sheet base composedof an elastomer and conductive particles exhibiting magnetism containedin the sheet base in a state oriented so as to arrange in rows in athickness-wise direction of the sheet base, and dispersed in a planedirection thereof, wherein supposing that a volume resistivity in thethickness-wise direction under an unpressurised state is R₀, and avolume resistivity in the thickness-wise direction in a statepressurised under a pressure of 1 g/mm² in the thickness-wise directionis R₁, the volume resistivity r₁ is 1×10⁷ to 1×10¹² Ω·m, and a ratio(R₀/R₁) of the volume resistivity R₀ to the volume resistivity R₁ is1×10¹ to 1×10⁴:
 2. The anisotropically conductive sheet according toclaim 1, wherein the volume resistivity R₀ is 1×10⁹ to 1×10¹⁴ Ω·m
 3. Theanisotropically conductive sheet according to claim 1, wherein a surfaceresistivity is 1×10¹³ to 1×10¹⁶ Ω/□.
 4. The anisotropically conductivesheet according to claim 1, wherein the total area proportion occupiedby a substance forming the conductive particles detected by theelectronic probe microanalysis in one surface of the sheet is 15 to 60%.5. An anisotropically conductive sheet comprising a sheet base composedof an elastomer and conductive particles exhibiting magnetism and avolume-resistivity of 1×10² to 1×10⁷ Ω·m contained in the sheet base ina state oriented so as to arrange in rows in a thickness-wise directionof the sheet base, and dispersed in a plane direction thereof.
 6. Theanisotropically conductive sheet according to claim 5, wherein theconductive particles are composed of ferrite.
 7. The anisotropicallyconductive sheet according to claim 5, wherein, a non-magneticconductivity-imparting substance is contained in the sheet base.